src/llvm/include/llvm/CodeGen/JumpInstrTables.h

   1 //===-- JumpInstrTables.h: Jump-Instruction Tables --------------*- C++ -*-===//
   2 //
   3 // This file is distributed under the University of Illinois Open Source
   4 // License. See LICENSE.TXT for details.
   5 //
   6 //===----------------------------------------------------------------------===//
   7 ///
   8 /// \file
   9 /// \brief An implementation of tables consisting of jump instructions
  10 ///
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_CODEGEN_JUMPINSTRTABLES_H
  14 #define LLVM_CODEGEN_JUMPINSTRTABLES_H
  15
  16 #include "llvm/ADT/DenseMap.h"
  17 #include "llvm/Pass.h"
  18 #include "llvm/Target/TargetOptions.h"
  19
  20 namespace llvm {
  21 class Constant;
  22 class Function;
  23 class FunctionType;
  24 class JumpInstrTableInfo;
  25 class Module;
  26
  27 /// A class to manage a set of jump tables indexed on function type. It looks at
  28 /// each function in the module to find all the functions that have the
  29 /// jumptable attribute set. For each such function, it creates a new
  30 /// jump-instruction-table function and stores the mapping in the ImmutablePass
  31 /// JumpInstrTableInfo.
  32 ///
  33 /// These special functions get lowered in AsmPrinter to assembly of the form:
  34 /// \verbatim
  35 ///   .globl f
  36 ///   .type f,@function
  37 ///   .align 8,0x90
  38 /// f:
  39 ///   jmp f_orig@PLT
  40 /// \endverbatim
  41 ///
  42 /// Support for an architecture depends on three functions in TargetInstrInfo:
  43 /// getUnconditionalBranch, getTrap, and getJumpInstrTableEntryBound. AsmPrinter
  44 /// uses these to generate the appropriate instructions for the jump statement
  45 /// (an unconditional branch) and for padding to make the table have a size that
  46 /// is a power of two. This padding uses a trap instruction to ensure that calls
  47 /// to this area halt the program. The default implementations of these
  48 /// functions call llvm_unreachable, except for getJumpInstrTableEntryBound,
  49 /// which returns 0 by default.
  50 class JumpInstrTables : public ModulePass {
  51 public:
  52   static char ID;
  53
  54   JumpInstrTables();
  55   JumpInstrTables(JumpTable::JumpTableType JTT);
  56   virtual ~JumpInstrTables();
  57   bool runOnModule(Module &M) override;
  58   const char *getPassName() const override { return "Jump-Instruction Tables"; }
  59   void getAnalysisUsage(AnalysisUsage &AU) const override;
  60
  61   /// Creates a jump-instruction table function for the Target and adds it to
  62   /// the tables.
  63   Function *insertEntry(Module &M, Function *Target);
  64
  65   /// Checks to see if there is already a table for the given FunctionType.
  66   bool hasTable(FunctionType *FunTy);
  67
  68   /// Maps the function into a subset of function types, depending on the
  69   /// jump-instruction table style selected from JumpTableTypes in
  70   /// JumpInstrTables.cpp. The choice of mapping determines the number of
  71   /// jump-instruction tables generated by this pass. E.g., the simplest mapping
  72   /// converts every function type into void f(); so, all functions end up in a
  73   /// single table.
  74   static FunctionType *transformType(JumpTable::JumpTableType JTT,
  75                                      FunctionType *FunTy);
  76 private:
  77   /// The metadata used while a jump table is being built
  78   struct TableMeta {
  79     /// The number of this table
  80     unsigned TableNum;
  81
  82     /// The current number of jump entries in the table.
  83     unsigned Count;
  84   };
  85
  86   typedef DenseMap<FunctionType *, struct TableMeta> JumpMap;
  87
  88   /// The current state of functions and jump entries in the table(s).
  89   JumpMap Metadata;
  90
  91   /// The ImmutablePass that stores information about the generated tables.
  92   JumpInstrTableInfo *JITI;
  93
  94   /// The total number of tables.
  95   unsigned TableCount;
  96
  97   /// The type of tables to build.
  98   JumpTable::JumpTableType JTType;
  99 };
 100
 101 /// Creates a JumpInstrTables pass for the given type of jump table.
 102 ModulePass *createJumpInstrTablesPass(JumpTable::JumpTableType JTT);
 103 }
 104
 105 #endif /* LLVM_CODEGEN_JUMPINSTRTABLES_H */